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Here's some possible good news out of New Zealand. So far only one study in 2006 with surprising results. I wonder why this study has not been repeated in other rivers to see if this a real finding.

Dydimo effects on river invertebrates: not as bad as feared?

"The researchers found that, in the didymo-affected rivers, the invertebrate drift density and biomass was actually highest at the sites with intermediate (in autumn) and highest (in winter) levels of didymo biomass. But the survey also confirmed that the invertebrate biomass contained a higher proportion of smaller species than is usually found in non-affected rivers, an effect that was more pronounced where volumes of didymo were higher.

While this effect was observed, the researchers said that, based on bioenergetics modelling, their results did not show that didymo affected invertebrate drift enough to negatively affect growth potential of drift-feeding brown trout.

This is encouraging news for anglers, but the Cawthron Institute researchers said that their results had to be interpreted with caution, because they were based on sampling in autumn and winter only, and limited to three sites."